Abstract

Abstract

Liganden-Stehblues: In einem Dieisenkomplex mit unsymmetrischem Brückenligand wurde unerwartet das verbrückte Intermediat der Wanderung eines Phosphorliganden zwischen den beiden Metallzentren beobachtet. Der Prozess verläuft ähnlich wie die Wanderung eines Carbonylliganden, ist aber so langsam, dass er NMR-spektroskopisch untersucht werden kann.

Der selten begangene Weg: An der Copolymerisation von Iminen und Kohlenmonoxid als Weg zu Polypeptiden besteht seit langem großes Interesse; sie ließ sich jedoch schwierig verwirklichen, weil geeignete Katalysatoren fehlten. Nun gelang es erstmals, diese Reaktion durchzuführen, und zwar mit einem einfachen Cobaltkatalysator (siehe Schema).

Slow dance: Long believed to be impossible, migration of a phosphorus ligand via a bridging intermediate is observed between two metal centers in a diiron complex containing an asymmetric bridging ligand. This process occurs in a similar fashion to the migration of carbonyl ligands but at a rate slow enough to be studied by NMR spectroscopy.

The path less taken: Copolymerization of imines and carbon monoxide has long been highly desirable as a route to synthesize polypeptides, but has been difficult to implement because of the lack of appropriate catalysts. This reaction has now been realized for the first time by using a simple cobalt catalyst (see scheme).

1,2-Diphenyl-1,2-dimethyldisilanylene-bridged bis-cyclopentadienyl complex [η⁵,η⁵-C₅H₄PhMeSiSiMePh-C₅H₄]Fe₂(CO)₂(μ-CO)₂ (1) was synthesized by a modified procedure, from which the trans-isomer 1b that was previously difficult to obtain has been isolated for the first time. More interestingly, two new regio-isomers [η⁵,η⁵-C₅H₄SiMe(SiMePh₂)C₅H₄]Fe₂(CO)₂(μ-CO)₂ (2) and [η⁵,η⁵-C₅H₄Me₂SiSiPh₂C₅H₄]Fe₂(CO)₂(μ-CO)₂ (3) were occasionally obtained during above process, the novel structures of which opened up new options for further study of this type of Si–Si bond-containing transition metal complexes. The molecular structure of 2 has been determined by the X-ray diffraction method.

The reaction of the title cyclic complex (1) with sodium amalgam in THF resulted in the expected cleavage of the Fe—Fe bond to afford bis-sodium salt (Me₂SiSiMe₂) [η⁵-C₅H₄Fe (CO)₂Na]₂ (4). The latter was not isolated and was used directly to react with MeI, PhCH₂Cl, CH₃C(O)Cl, PhC(O)Cl, Cy₃SnCl (Cy = cyclohexyl) or Ph₃SnCl to afford corresponding ring-opened derivatives (Me₂SiSiMe₂) [η5-C₅H₄Fe (CO)₃R]₂ [5, R=Me; 6, R = PhCH₂; 7, R = CH₃C(O); 8, R = PhC (O); 9, R = Cy₃Sn or 10, R = Ph₃Sn]. The crystal and molecular structures of 10 were determined by X-ray diffraction analysis. The molecule took the desired anti conformation around the Si—Si bond. The length of the Si—Si bond is 0.2343(3) nm, which is essentially identical to that in the cyclic structure of 1 [0.2346(4) nm]. This result unambiguously demonstrates that the Si—Si bond in the cyclic structure of 1 is not subject to obvious ring strain.